Or, perhaps they're norming to their local context. In any case, Andrew Gelman pointed to Boris Shor's site, who then linked to his research on ideology, which led me this working paper, All Together Now: Putting Congress, State Legislatures, and Individuals in a Common Ideological Space. Here's what jumped out at me:

I have also found that the common space scores perform exceedingly well as a predictor of individual vote choice compared with even a non-naive three item composite ideology. The common space scores even do as well or better than party identication in predicting both presidential and congressional voting. In fact, conventional denitions of ideology, predicated on self-reporting, show themselves to be completely inadequate.

The "common space scores" is derived from Project Vote Smart's NPAT.

Labels: politics